This invention relates generally to commercial refrigeration and more particularly to a commercial refrigeration system having unique power and communication wiring, as well as distribution of control intelligence features.
Great advances have been made over the last 50 years in all aspects of refrigerated food store merchandisers and coolers and the various commercial systems therefor. Retail food merchandising is conducted to a great degree in large supermarkets, each requiring substantial refrigeration capacity. For example, a 50,000 square foot (4,650 square meter) supermarket may have refrigerated display fixtures and other coolers and preparation rooms requiring an aggregate refrigeration capacity in excess of 80 tons (1,000,000 BTU/hr. or 242,000 kcal/hr.) which may include over 20 tons (60,500 kcal/hr.) of low temperature refrigeration at evaporator temperatures in the range of −35° F. to −5° F. (−37° C. to −21° C.) and over 60 tons (181,500 kcal/hr.) of normal temperature refrigeration at evaporator temperatures in the range of 15° F. to 40° F. (−9° C. to 4° C.). Such present commercial refrigeration systems have a multitude of evaporator cooling coils for the various refrigerated product merchandisers located throughout the supermarket; and these evaporators are typically cooled by several multiplexed low temperature and medium temperature compressor systems. It is also known to use such systems in smaller environments such as convenience stores, or for the preservation of other perishables not related to the food store environment (e.g., blood, plasma, medical supplies).
Conventional practice is to put the refrigeration requirements of a supermarket into two or more multiplexed refrigeration systems—one for the low temperature refrigeration fixtures for refrigerating fresh foods including meat, dairy and produce at product temperatures in the range of 28° F. to 50° F. (−2° C. to 10° C.). Each such system is a closed system branch having a single condenser/receiver and common discharge suction and liquid distribution headers with parallel circuits of the latter to the respective merchandiser or cooler evaporators and with the various complex valving requirements to balance suction pressures (EPR valves) and to accommodate selective evaporator isolation for gas or other types of defrosting. In any event, the multiplexed compressors of such systems are usually installed in back machine rooms and typically connect to roof top air-cooled condensers, which in turn connect back to the machine room to a receiver and thence to the liquid refrigerant distribution header and various high side valving and liquid line circuit outlets.
The multiplexed compressors in a refrigeration system are typically mounted together on a rack and piped in parallel, each having a low side connected to a suction header and a high side connected to the discharge header. The operation of the compressors is cycled, based on a measured system parameter, to maintain a desired level of refrigeration. Usually, the measured parameter is suction pressure at the suction header. A transducer on the suction header provides a signal to a compressor controller indicating the suction pressure, and the controller compares the measured pressure with a setpoint pressure and turns the compressors off and on accordingly, taking into consideration other factors such as compressor run time. It is also known to adjust system capacity in other ways, such as by changing the speed of an individual compressor motor where the design of the compressor permits. Refrigeration level can also be affected by cycling condenser fans and in other ways not directly pertaining to the compressors.
In addition to the controller, each compressor has a high voltage protection circuit capable of shutting down the compressor when it operates outside any one of a number of predetermined safe operating limits. A high voltage line in a shielded conduit must be brought from the store utility power distribution center to the compressor where the protection circuit is located. The protection circuit normally energizes a compressor control coil to close a compressor contact in series with the compressor power line so that the compressor may run when activated by a relay operated by the controller. Operating limits are typically established for one or more of: motor winding temperature, oil level (or pressure), discharge pressure and phase loss/reversal. The protection circuit has a safety contact wired in series for each operating limit. When a particular operating limit as detected by a corresponding sensor is exceeded, the contact opens causing the control circuit to open, de-energizing the compressor contactor coil and disabling energization of the compressor by the controller.
Existing protection circuits are aware only that the operating limit has been traversed, and have no capability to provide information as to the actual value of the parameter. A separate alarm circuit from the controller to the control circuit is needed so that notification of the problem can be made. In order to know which operating limit was traversed, still more indicator circuits are required between each safety contact and the controller. Thus, a substantial amount of wiring is necessary to connect the compressor to the controller. Even if the protection circuit is so wired for providing maximum information, there are substantial gaps in information concerning the operation of the compressor because of the absence of the ability to give an absolute reading of the parameter measured.
A parallel switchback circuit may be wired in parallel to the controller so that electro-mechanical control of the compressor can be activated in the event of controller failure. The parallel switchback circuit allows a suction pressure control switch to activate the compressor in the absence of a functioning controller. The switchback circuit provides only crude system control subsequent to controller failure. In order to have such a circuit it will be necessary to install isolation relays to prevent the possibility of control interference from the switchback circuit when the controller is operating normally.
In addition to the control wiring described above, power wiring is also necessary. The compressor is powered by a high voltage, three phase 480V AC or 208V AC line (or various other three phase power sources)and the control circuit is powered by a single phase 120V AC or 208V AC high voltage line. Two high voltage lines must be wired for each compressor; one three phase for the compressor motor and one single phase line for the protection circuit. These lines are required to be shielded, such as by placement in a conduit. Thus, a number of shielded power lines are required for each compressor rack, making existing wiring complex and costly.
Most of the sensors now used for monitoring safety and control parameters for the compressors are located outside of the compressor. Suction pressure monitoring is typically from the suction header, substantially remote from the compressors. Sensors associated with the safety module are located on the compressor. Thus, all of these items are exposed to potential damage during shipping and installation.
Further, it is also desirable to monitor and/or control other valving, switching circuits, and sensors associated with each refrigeration branch in a typical multiplexed system. For example, it is desirable to monitor actual fixture temperature to ensure that perishable products are being stored at an appropriate temperature to prevent spoilage. In prior art systems, however, a large amount of wiring is required to provide appropriate interfaces between the compressor rack and the various control valves, switches, and sensors in a given system. The wiring is a complex task and the source of frequent system malfunction, particularly for newly installed refrigeration systems. Such wiring requirements include power wiring, which requires additional shielding and protection techniques, including channeling the wiring through protective conduit.
Examples of the such valving, switching circuits, and sensors that have been used in prior art refrigeration systems may be found in several patents which are owned by the assignee of the present invention. For example, Thomas et al., U.S. Pat. No. 5,743,102, the entire disclosure of which is incorporated herein by reference, discloses a system having modular secondary refrigeration. Such system includes a cooling source remote from the refrigeration units that is constructed and arranged for circulating a fluid coolant in heat exchange relationship with the condenser to obtain optimum condensing and efficiency. FIG. 4 of the Thomas et al. patent discloses various valves and flow control mechanisms suitable for use in such a secondary refrigeration system. Schaeffer et al., U.S. Pat. No. 5,440,894, the entire disclosure of which is incorporated herein by reference, discloses a strategic modular commercial refrigeration system in which multiplexed compressors are placed in close proximity to one or more fixtures.
Shapiro, U.S. Pat. No. 6,067,482, the entire disclosure of which is incorporated herein by reference, discloses a load shifting control system for a commercial refrigeration system. As disclosed therein, a processor is configured to select a preferable combination of loads, and to generate control signals so as to achieve an allocation of loads between power sources. FIG. 3 of the Shapiro patent is illustrative of a commercial refrigeration system in accordance with a preferred embodiment of that invention.
Several other patents identify various structures, systems, and methods for defrosting a refrigeration system. Among such patents is Quick, U.S. Pat. No. 3,343,375, the entire disclosure of which is incorporated herein by reference, discloses a latent heat refrigeration defrosting system. In particular, the Quick patent discloses a system for defrosting evaporators using the latent heat of saturated compressed gasses. FIG. 1 of the Quick patent is exemplary of such a system. Further, Behr et al., U.S. Pat. No. 5,921,092, the entire disclosure of which is incorporated herein by reference, discloses a fluid defrost system and method that is suitable for use in secondary refrigeration systems, such at the system disclosed in the Thomas et al. Patent, which is discussed above. FIGS. 1 and 2 of the Behr et al. patent are illustrative of aspects of that invention, including the control valves and switching associated with such a system.
Still other patents disclose various structures, systems, and methods related to controlling the oil used in a commercial refrigeration system. Included among these patents is DiCarlo et al., U.S. Pat. No. 4,478,050, the entire disclosure of which is incorporated herein by reference. The DiCarlo et al. patent discloses an oil separation system, including control means for maintaining a predetermined oil level in the compressor. FIG. 1 of the DiCarlo et al. patent is believed to be illustrative of a typical commercial refrigeration system embodying such a system, including the control valves and switches used in the system. A related patent by DiCarlo et al., U.S. Pat. No. 4,503,685, the entire disclosure of which is incorporated herein by reference, discloses an oil control valve, suitable for use in an oil separation and delivery system of a refrigeration system. Yet another related patent by DiCarlo et al., U.S. Pat. No. 4,506,523, the entire disclosure of which is incorporated herein by reference, discloses an oil separator unit, suitable for use in an oil separation and return system of a refrigeration system.
In view of the foregoing, there is a need for a commercial refrigeration system which reduces the need for power wiring between system components. There is a further need for such a system in which subsystem control is distributed among several modules, thereby reducing the risk of failure and the adverse consequences should a failure occur. There still a further need for a commercial refrigeration system that is at least partially self-configuring and is more easily installed and operated, as compared to prior art control systems.